Remote control system



Aug. 10,1948.

H. O. PETERSON REMOTE CONTROL SYSTBI Filed Jan. 22, 1945 .IMMIP o,... e...

Patented Aug. 10, 1948 REMOTE CONTROL SYSTEM Harold 0. Peterson, Riverhead, N. Y., anignor to Radio Corpm'ation of America, a corporation of Delaware Application January zz, ms, serai No. 413,1

1 Cahn. (cl. sis-za) This invention relates to a new and useful remote control or indicating system.

An object of this invention is to provide a simple means of controlling and/or indicating an operation or the position of a device remotely located over a single pair of wires where the two terminals of the circuit are operated on the same alternating current power line.

Another object of this invention is to provide a control system in which radio circuit variable elements such as rotary condensers and the like may be controlled from a distant point.

A feature of this invention is means excited by polyphase currents including rotor devices and a balanced modulator for controlling from a control point the angular position-of a rotor driven element at the controlled point, with an indicator at the control point the angular motion of which is duplicated by the rotor at the controlled point.

It is often desired to control or indicate an operation of any suitable variable device at a distance over a single pair of wires, and while there are numerous methods known to the prior art, such methods often require the use of complicated movable devices and numero'us circuit elements. By my device a simple, inexpensive and emcient method is devised.

This invention will best be understood by referring to the accompanying drawing which shows a circuit diagram of the remote control ,system of this invention. VPolyphase or threephase alternating current power from the same central network appears at the inputs I and 2. The inputs I and 2 may be located at points at a distance from each other. The source of A.-C. power input I is indicated as a-single phase source and may be one phase of the three phase input supplied at the unit 2. If a threephase power source is not available, it may be developed locally from single phase current and supplied at the unit 2 by any suitable phase splitting means. The three-phase power input at 2 isconnected to a device 3 including threephase stator or fixed delta coil windings I and a rotor coil winding 5. A manual control i is coupled to a shaft 1 which rotates rotor coil winding B and also an indicator l. Note that the gearing between control i and indicator l may be such that control 6 rotates a number of times for each rotation of l. The output leads from the rotor winding of device 3 connect to a line 0 extending-tothe distant point.

The use of three-phase power system at the control point is merely a. matter of convenience in providing the input for device I from which I an outputof variable"phase and/or frequency may be derived.

At the other terminal of the improved system where the vvariable elements are to be controlled a feed transformer Il has its primary II -connected to control line 2. The input source I of the controlled point is connected to the primary windings of two'transformers I2 and Il the secondary windings of which couple balanced modulators in push-pull relation. A variable phase shifter network Il is connected between the primary winding of transformer Il and unit I to change the A.-C. voltage exciting the primary winding of transformer II in approximately 90 phase displaced relation with respect to the excitation of the primary winding of transformer I2. The secondaries of input transformers I2 and Il areconnected to the input grids of four three-element tubes Ii, It, I1 and Il which are arranged to serve as balanced modulators.

One balanced modulator comprises tubes Il and I0 having their control grids excited differentially (push-pull) by A.C. in the secondary winding of transformer I2 and having their anodes coupled to winding 26 of a controlled motor. The other balanced modulator comprises the tubes I1 and Il having their control grids excited in pushpull relation by A.C. from the secondary winding of transformer I2 and having their anodes coupled to field winding 2|,of the controlled motor. The pushpull excitation of the grids of tubes I1 and Il is displaced about 90 with respect to the excitation of the grids of tubes IB and I6 because of the action of phase shifter I4. The windings 2i and 2O are angularly disposed.

The secondary windings of transformers I2 and I3 both are connected at their midpoints to the secondary winding of the transformer Il which is also connected to a bias source I! connected by ground to the cathodes of all of the tubes to maintain the grids slightly above ground and cathode potential. The fundamental frequency of the power line inputs I and 2 is suppressed or' filtered out by four low pass filters 2|, 22, 22 and 2l so that only the difference frequency is supplied by the balanced mod-r ulators to windings 25 and 2C of a motor. lThe windings 25 and 28 have midpoint taps for supplying current from a D.C. source 21 to-the anodes of the balanced modulator tubes. A

D.-C. source II. The motor may be made up Y with a ytoothed rotor II arranged in the field of windings II and II in such a manner that it will rotate at a speed corresponding to the difference between the frequencies supplied from source I and the land control line I. A shaft II is secured to rotor II and arranged to be coupled to the variable device not shown which is to be controlled from the point I.

An indicator Il is employed to indicate the position of the variable device.

The purpose of having an indicator at the control point which is so arranged as to give the same reading as an indicator at the controlled point is, of course, to provide the operator at the control point a physical picture of what he is controlling.

In the operation of this system, if the rotor coil I of the device I is rotated mechanically by manual operation in one direction, there will appear in it a frequency which is higher than that of the power supply I, and if the rotor coil I is rotated in the other direction, a frequency which is lower than that of the power line will result in secondary I. When the secondary of device I is maintained at a constant mechanical position there is induced in it a voltage of constant phase relative to the phase of the voltage in the primary. When secondary I is rotated in one direction the phase of the voltage in it is advanced. If it is rotated fast enough to produce a phase advance of 360 degrees per second, it is equivalent to producing a new frequency one cycle per second greater than the frequency on the primary voltage. The same reasoning, of course, applies to rotation in the opposite direction and at other angular rates. The overall operation of the system is. in fact, such that the rotor II of motor I5 is locked in step with position of the rotor I of device I.

The A.-C. power from source l is transmitted through the primaries of transformers II and II in push-pull relationship tothe grids of the balanced modulators. The A.C. voltage feeding the transformer II is changed in its angular phase position approximately 90 degrees by network II.

vThe grids of both balanced modulators are also excited in parallel by A.C. from line I through transformer II.

When the rotor I is stationary and properly oriented in respect to its coupling to the threephase windings at I currents of equal'frequencies and phases (excepting as displaced as described above) are fed to the two balanced modulators and zero beat output is derived from the modulators. The windings II and II are then subject to steady or D.C. currents and rotor II is stationary. The gearing between rotor II and indicator Ii and between rotor I and indicator I is arranged so that the angular position of indicator Il is related as desired with respect to the angular position of indicator I. Now if we rotate winding I in one direction the frequency of rotation thereof is added to the line frequency and the modulators now supply to the motor windings two phase beat notes of a frequency equal to the rate of rotation of rotor l. The beat note currents through the windings II and II causes II to rotate Just as winding I was rotated. Due to the step up in the gearing between rotor I and indicator I, and between rotor II and indicator Il the rotors may rotate a number cf times for each rotation of the indicators.

Now if rotor l is rotated in the opposite direction there is a phase reversal of the beat notes (because when rotor I is rotated in one direction cycles are added to the line frequency while rotation of I in the opposite direction subtracts cycles from the line frequency) and the rotor II rotates in the opposite direction to follow the angular movement of rotor I. The higher the beat note frequency the higher the rate of rotation of rotor II.

The system responds to fractions of a cycle of rotation of rotor I, i. e., phase changes in the manner as described above.

I have found that a motor which will operate in a satisfactory manner in this system is an iron cored motor known as the Alnico type". The motor used here is of the hysteresis type wherein` the rotor is of a magnetic material known widely in the electrical art under the registered trade name of Alnico. The motor used had two windings represented by numerals Il and II and these windings of the motor were provided with midtaps for supplying the plate current to the balanced modulators. Satisfactory control of the motor is obtained.

As the power line frequency is suppressed in the windings of motor II by low pass filters Il, II, II and II only the difference in frequency operates or actuates the motor II. Therefore, as a result when the frequencies in the source I and line I are exactly equal, the rotor II of motor II will be stationary. When the rotor of device I is moved, the phase of the voltage transmitted over the transmission will be changed and the rotor II of motor II will then assume a new position. Thus it will be seen from this device that it is possible, by turning control I, to cause a corresponding rotation of shaft II. If desired, gears may be arranged so that indicator Il will have the same reading as indicator I.

Multiplication of the frequency transmitted on transmission line I may be desirable in some instances to produce a frequency more suitable for transmission over the particular transmission circuit at hand. Also it may in some cases be used as a means for stepping up the sensitivity of the control system since the angular displacement of a voltage is multiplied by the same factor as the factor by which its frequency is multiplied.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modincations may be made without departing from the scope of my invention, as set forth in the appended claim.

What I claim is: p

In apparatus for controlling the position of an element, a motor having a rotor linked by driving means with said element, said motor having windings angularly related, a source of alternating current, two converter stages, each having an output. leads connecting the output of one converter stage to one winding and the out put of the other converter stage to the other winding, connections from said source to each converter for exciting the same by alternating current, a phase shifter in one of said connections, apparatus for supplying Dolylihase currents, of the same frequency as the currents of said source, to angularly related windings, a rotor winding in the neld of said angularly related windings, connections from said rotor winding to each converter for exciting the same by alternating current of the same frequency as the alternating currents of said source when said rotor winding is stationary, the arrangement being such that the converters then supply zero beat notes to said motor windingsl means for rotating the rotor winding in the desired direction at the desired rate, whereby said converters supply beat notes to said motor windings the phase of whichl denotes the direction of rotation of the rotor winding and the frequency of which depends on the rate of rotation of the rotor winding, and an indicator the position of which is iixedly related to the position of said rotor winding.

. HAROLD O. PETERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

